The invention comprises a pulsating mercury drop to obtain polarographic, voltametric (coulometric), potentiometric, and anodic stripping measurements, and other measurements derived therefrom. A pulsating mercury drop is extruded from a capillary tube into an electrochemical solution to be evaluated, and its electrolytic current or potential is measured against a reference electrode. The method provides that mercury is extruded from the capillary (and the size of the drop is increased) and then it is withdrawn back into the capillary (and the drop is decreased to its original size), so that the drop pulsates at a frequency of 0.1 to 100 cycles/second. In addition, the potential of the drop is varied continuously, or is changed by a jump from a value where oxidation or reduction of the measured electrochemical compound occurs, to a value where anodic dissolution results in deposition of the measured compound.
A known device is described in Dias et al, Pulsed Flow mercury Electrode, J. Electroanal. Chem. No. 130, pp 345-9 (1981).
Polarographic measuring devices are known, and are based on principals first developed by the Czechoslovak chemist Jaroslav Heyrovsky. In its simplest form, a polarograph is an instrument that photographically records minute changes in the intensity of a current resulting from a gradually increasing applied voltage, in electrolysis with a dropping mercury cathode. The polarograph is typically used to measure the deposition or reduction of cations and anions, voltage gradients, solubility, ionic complexity; and is useful for qualitative and quantitative microanalysis.
Voltametric, or coulombic analysis is also known as a method of measuring current intensity by electrolysis. Potentiometric analysis relates to the continuous measurement of the potential of an electrode immersed in a solution to be evaluated. A rapid change in potential typically indicates the end of the electrochemical reaction.
A polarographic measurement of a dropping mercury electrode may be obtained by known methods, whereby the regeneration of surface compounds and the removal of deposited compounds is evaluated by reference to the dripping mercury; with the measurements carried out on a fresh mercury surface. Suitably reproducible results can be obtained with this method, but the relatively rapid consumption of mercury, which must be purified prior to each use, is a distinct disadvantage. From the electrochemical point of view, another disadvantage is that the newly created drop must be electrically charged to a measurement potential. This charge becomes manifest as a capacity current that is summed with the faradic current corresponding to the electrochemical oxidation/reduction potential of the measured compound. The added charge reduces the sensitivity of the method and device.
Numerous methods of avoiding the charging current have been suggested. For example, one method would be to measure against a small changing surface of mercury, or against a stationary mercury drop.